Tacrine

Identification

Name

Tacrine

Accession Number

DB00382 (APRD00690)

Type

Small Molecule

Groups

Investigational, Withdrawn

Description

A centerally active cholinesterase inhibitor that has been used to counter the effects of muscle relaxants, as a respiratory stimulant, and in the treatment of Alzheimer's disease and other central nervous system disorders. Tacrine has been discontinued for the United States market.

Pharmacology

Indication

For the palliative treatment of mild to moderate dementia of the Alzheimer's type.

Pharmacodynamics

Tacrine is a parasympathomimetic- a reversible cholinesterase inhibitor that is indicated for the treatment of mild to moderate dementia of the Alzheimer's type. An early pathophysiological feature of Alzheimer's disease that is associated with memory loss and cognitive deficits is a deficiency of acetylcholine as a result of selective loss of cholinergic neurons in the cerebral cortex, nucleus basalis, and hippocampus. Tacrine is postulated to exert its therapeutic effect by enhancing cholinergic function. This is accomplished by increasing the concentration of acetylcholine at cholinergic synapses through reversible inhibition of its hydrolysis by acetylcholinesterase. If this proposed mechanism of action is correct, tacrine's effect may lessen as the disease progresses and fewer cholinergic neurons remain functionally intact. There is no evidence that tacrine alters the course of the underlying dementing process.

Mechanism of action

The mechanism of tacrine is not fully known, but it is suggested that the drug is an anticholinesterase agent which reversibly binds with and inactivates cholinesterases. This inhibits the hydrolysis of acetylcholine released from functioning cholinergic neurons, thus leading to an accumulation of acetylcholine at cholinergic synapses. The result is a prolonged effect of acetylcholine.

Overdosage with cholinesterase inhibitors can cause a cholinergic crisis characterized by severe nausea/vomiting, salivation, sweating, bradycardia, hypotension, collapse, and convulsions. Increasing muscle weakness is a possibility and may result in death if respiratory muscles are involved. The estimated median lethal dose of tacrine following a single oral dose in rats is 40 mg/kg, or approximately 12 times the maximum recommended human dose of 160 mg/day.

Taxonomy

Description

This compound belongs to the class of organic compounds known as acridines. These are organic compounds containing the acridine moiety, a linear tricyclic heterocycle which consists of two benzene rings joined by a pyridine ring.